Valves and valve assemblies are commonly used to control the flow of a fluid. One application for such valves is in fluid filtration wherein the fluid flows through a valve body and the filtering medium is a replaceable cartridge-type filter. Such filters may be used to remove particulates from the gas or liquid flowing through them. In other applications, such filters are used to remove droplets of water, oil or other contaminants from a stream of gas which flows through the filter.
Various types of valve assemblies for use on filtering applications are shown in U.S. Pat. Nos. 3,777,889; 4,092,673 and 4,731,183. The valve assemblies shown therein have a valve body with an attached canister or housing and are used to control the flow of fluid through a replaceable cartridge filter housed in the canister. Such known assemblies have a common disadvantage in that they require that fluid flow be entirely shut off when the filter is being replaced. In many filtration applications, residential and commercial water systems for example, it is usually considered more desirable to have unfiltered water available than to have the water supply interrupted, even for a relatively short period of time.
Similar types of valve assemblies are shown in U.S. Pat. Nos. 3,306,451; 3,853,761; 3,907,688; 3,935,106 and 4,271,020. The valves shown in these latter patents provide the additional capability of maintaining the continuity of fluid flow, even during those occasions when the filter cartridge is being changed. Such valves are often said to have a "bypass" capability in that in one position, fluid flow bypasses the chamber in which the filter is housed The cartridge can be easily changed without interruption of service and, equally important, without serious leakage or spillage of fluid to the surrounding area.
However, many of the valves shown in the foregoing patents share a common disadvantage in that they rely for their flow directing and fluid sealing capabilities upon parts which have large sealing areas and make sliding contact with one another. Such parts must necessarily be closely and accurately fitted to provide an adequate fluid seal since their sealing surfaces are not resilient. That is, because of the rigidity of the parts and of the necessity to effect a good seal, there is relatively little "forgiveness" in their manufacturing tolerances.
In addition, the valves shown in all of the foregoing patents require a substantial number of parts to construct them. This has adverse implications for the purchasing and inventory control functions and for the time required to assemble such valves. Thus, their final cost is necessarily adversely impacted.
Yet another disadvantage of the valve assemblies shown in certain of the foregoing patents relates to the fact that they are devoid of any pressure venting capability. Such capability is important since fluid flowing through the assembly is under pressure. When the cartridge filter is to be changed, pressure in the canister makes it difficult to unscrew or otherwise release the canister from the valve body unless pressure is first relieved.
A valve assembly which has both filtration and bypass capabilities, which incorporates parts readily constructed by plastic injection molding techniques, which uses resilient seal techniques to provide fluid sealing, which incorporates a pressure vent and which requires a minimum number of parts would be an important advance in the art.